Plugin breaking my theme

I have installed the plugin. When I fill the title on the add new page and the publish the page, the title runs over my right column sidebar instead of wrapping up with the post page space.

When I don’t fill the title of the post and then publish the page in that case I find </ such kind of symbol on left top corner of the page.

I have deleted the plugin and re-installed the theme and now everything is fine.

But wants this plugin so let me know how I can work out.

Thanks

https://wordpress.org/plugins/easy-digital-downloads/